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  Competing Interactions for Semiconductor Assembly   Electrochemical Deposition of Inorganic Semiconductors   Chiroptical Properties of Helical Electroactive Molecules
 
Imagine that a molecule or a macromolecule needs to be assembled into a structure or morphology that is rare or not preferred by the molecule. How can the molecule be directed to assemble the way we need it? Finding the answer to this question will have solved a very important problem in organic photovoltiac cells. Plus it will make a major impact in the prediction of condensed phase structures.

For efficient organic or hybrid photovoltaic cells, hole-conducting (blue in the figure) and electron-conducting (orange in the figure) organic moieties need to be assembled into segregated structures. This allows the exciton to split at the interface. Yet, it is favorable for hole-conducting moieties mix with electron-conducting moieties. How do we keep them separated?

Our approach involves appending groups to electron-rich and electron-poor moieties such that the interaction between these groups will be unfavorable. The underlying hypothesis of our approach is that mixing of electron-rich and electron-poor moieties will be disfavored because of the immisciblity between the groups appended on them.

Impact of our Work: Fundamental understanding of how competing interactions direct condensed phase structures, and Segregated morphologies for efficient organic photovoltaic cells.

For more details, see our Group Wiki site.

 
Can we synthesize crystalline inorganic semiconductors using electrochemistry and at room temperatures? Generally, inorganic semiconductors are synthesized at very high temperatures. We became interested in using electrochemical deposition when we encountered the problem of growing semiconductor nanorods perpendicular to the surface of electrodes for photovoltaic applications.

In hybrid photovoltaic cells, semiconductor nanorods are used as electron conductors. For efficient charge transport, the length of the rods should be on the order of micrometers and the width of the rod should be in nanometers. Moreover, the semiconductor rods should be oriented perpendicular to the electrode surface for efficient charge collection.

Our approach involves the use of electrochemical deposition within the pores of a nanoporous template and the removal of template after the deposition. Our work involves optimization of electrochemical conditions to obtain the targeted phase of the semiconductors in a crystalline form and fabricate photovoltaic devices.

Impact of our work: Methods for obtaining crystalline inorganic semiconductors at ambient, kinetic conditions through templated epitaxial growth, and Synthesis of oriented inorganic semiconductors for efficient hybrid photovoltaic cells.

For more details, see our Group Wiki site.

  
In 2006, our group and Barnes' group reported the chiroptical response of single, conjugated helical triarylamine molecules. This study led to our groups to ask some fundamental questions: What factors affect optical rotation, circular dichroism or circularly polarized luminescence in molecules? Solvent? Orientation? Local environment? Other factors? If so, why and how?

Chiroptical properties has been used to understand the absolute structure of molecules and macromolecules. However, the absolute value of the chiroptical property, say optical rotation, changes dramatically depending on various factors. For example, a chiral compound may have an optical rotation of (+)100 in one solvent and (-)100 in an another solvent.

We are synthesizing helical molecules with specific functionalities to anchor them on surfaces. In collaboration with Prof. Barnes and his group, we are studying the single molecule chiroptical spectroscopy of these molecules to find the answers a fundamental question: What factors affect chiroptical properties and how?

Impact of our work: Fundamental understanding of chiroptical properties, Fabrication of efficient polarized light emitting diodes, Fabrication of chiral surfaces, and Backlights for LCDs.

For more details, see our Group Wiki site.